Method and apparatus for fabricating quantum dot functional structure, quantum dot functional structure, and optically functioning device

ABSTRACT

The present invention is to fabricate a quantum dot functional structure having ultra-fine particles homogeneously distributed in a transparent medium by efficiently fabricating high-purity ultra-fine particles having a single particle diameter and uniform structure and depositing the ultra-fine particles onto a substrate in conjunction with the transparent medium. For these purposes, an apparatus for fabricating a quantum dot functional structure is provided. The apparatus comprises: an ultra-fine particle generating chamber for generating high-purity ultra-fine particles by exciting a semiconductor target with pulsed laser light in a low-pressure rare gas atmosphere, and then by allowing the semiconductor target to be detached or ejected by ablation reaction and condensed and grown in the gas; an ultra-fine particle classifying chamber for classifying the ultra-file particles; a depositing chamber for depositing the high-purity semiconductor ultra-fine particles and the transparent medium by exciting a transparent medium target with excimer laser light at the same time or alternately when the high-purity semiconductor ultra-fine particles are collected onto the substrate, and by collecting the substance generated through ablation reaction onto the substrate; and a carrier gas exhaust system.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to methods and apparatuses forfabricating quantum dot functional structures, quantum dot functionalstructures, and optically functioning devices. More particularly, thepresent invention relates to a method and an apparatus for fabricating aquantum dot functional structure, a quantum dot functional structure,and an optically functioning device, which provide the followingoutstanding features. The features make it possible to control thediameter of and alleviate the contamination of ultra-fine particles thatare expected to provide various functions resulting from the quantumsize effects. The features also make it possible to provide an improvedefficiency for the optically functioning device fabricated using aquantum dot functional structure, in the transparent medium of which theultra-fine particles are distributed homogeneously.

[0003] 2. Description of the Prior Art

[0004] To employ semiconductor ultra-fine particles formed of Sifamilies of IV materials for use in an optically functioning device thatcan emit light in the visible spectrum, it is indispensable to providespherical ultra-fine particles which are controlled on the order of onenanometer in diameter. Moreover, the laser ablation method is preferablyapplied to the fabrication of the ultra-fine particles on the order ofone nanometer in diameter.

[0005] For example, FIG. 1 is a conceptual view depicting an apparatus,disclosed in Japanese Patent Disclosure No. 9-275075, for applying thelaser ablation method to a conventional target material to fabricateultra-fine particles by deposition.

[0006] Referring to FIG. 1, a laser light beam is emitted from anexcimer laser source 1 and travels through an optical system constitutedby a slit 2, a condenser lens 3, a mirror 4, and a laser light inletwindow 5 to be guided into a vacuum reaction chamber 6, where the laserlight beam is focused on and thus radiates the surface of a targetmaterial 8 placed in a target holder 7, which is arranged inside thevacuum reaction chamber 6.

[0007] In addition, there is arranged a deposition substrate 9 in adirection normal to the surface of the target material 8. Substancesdetached or ejected from the target material 8 by laser ablation arecaptured or deposited on the deposition substrate 9.

[0008] An explanation will be given below in more detail to a case wheresemiconductor ultra-fine particles are fabricated with Si being employedas the target material in the apparatus configured as described above.

[0009] First, the vacuum reaction chamber 6 is pumped down to anultra-high vacuum of pressure 1×10⁻⁸ Torr by means of an ultra-highvacuum exhaust system 10, which is mainly constituted by aturbo-molecular pump, and then the ultra-high vacuum exhaust system 10is closed.

[0010] Subsequently, a helium (He) gas is introduced through a rare-gasguide line 11 into the vacuum reaction chamber 6. The vacuum reactionchamber 6 is held at a constant pressure (of 1.0 to 20.0 Torr) with thelow-pressure rare gas (He), the flow of which is controlled by means ofa mass-flow controller 12 and which is differentially exhausted by meansof a differential exhaust system 13 mainly consisting of a dry rotarypump. In the He gas atmosphere kept at a pressure of a few Torr, thesurface of the target material is radiated with a laser light beam of ahigh-energy density (e.g., 1.0 J/cm² or greater) to cause the substancesto be detached or ejected from the target material.

[0011] The detached substance gives kinetic energy to the surroundinggas molecules, which are in turn urged to condense and grow in the gasatmosphere into ultra-fine particles of a few to a few tens ofnanometers in diameter, the ultra-fine particles being deposited on thedeposition substrate 9.

[0012] Originally, since the IV-group semiconductors are an indirectbandgap material, their bandgap transitions cannot be dispensed withphonons. The materials naturally cause much heat to be generated intheir recombination, thus providing significantly decreased radiativerecombination probability. However, the material shaped in ultra-fineparticles having a diameter of a few nanometers causes the wave numberselection rule to be relaxed in bandgap transitions and the oscillatorstrength to be increased. This in turn increases the probability ofoccurrence of radiative electron-hole pair recombination, thereby makingit possible to provide intense light emission.

[0013] Here, the wavelength of emitted light (i.e., the energy ofemitted photons) is controlled by making use of an increase inabsorption edge emission energy (corresponding to bandgap Eg) providedby the quantum confinement effect resulted from a decrease in diameterof ultra-fine particles. FIG. 2 is an explanatory graph showing thecorrelation between the diameter of the aforementioned ultra-fineparticles and the absorption edge emission energy thereof.

[0014] That is, to emit light at a single wavelength, it isindispensable to make the diameter of the ultra-fine particles uniform.If ultra-fine particles of a diameter corresponding to the emissionwavelength can be generated and deposited within as narrow a diameterdistribution as possible, it is made possible to fabricate an opticallyfunctioning device for emitting light of a single color.

[0015] As described in the aforementioned prior art, it is required togenerate and deposit ultra-fine particles having a particle diameterdistribution controlled to provide a single diameter of a few nanometersin order to fabricate an optically functioning device for emitting lightat a single wavelength using semiconductor ultra-fine particles.

[0016] The prior art makes it possible to control the mean particlediameter by selecting as appropriate the pressure of an atmospheric raregas or the distance between the target material and the depositionsubstrate. However, the prior art provides a still broad particlediameter distribution. Thus, it is difficult to obtain semiconductorultra-fine particles of a uniform diameter distribution having, forexample, a geometric standard deviation 0 g of 1.2 or less.

[0017] That is, this means that more aggressive particle diametercontrol is required. In addition, nm-sized ultra-fine particles are verysensitive to the contamination of impurities or defects due to theirhigh surface atom ratio (e.g., about 40% at a particle diameter of 5nm).

[0018] That is, it is required to provide a clean and damage-lessprocess as a method for generating and depositing the particles.Moreover, adhering and depositing semiconductor ultra-fine particlesdirectly onto a deposition substrate as in the prior art would tend toresult in a thin film of a porous structure formed of a deposit ofultra-fine particles.

[0019] Suppose that electrodes are connected to such a porous structureto allow it to function as an optically functioning device. In thiscase, it may be required to optimize the structure somehow. On the otherhand, in order to derive the quantum size effect originally provided forspherical ultra-fine particles to implement a new optical functionrepresentative of light emission, further optimized shape and structuremay be required such as a structure having particles distributedhomogeneously in a stable transparent medium.

[0020] In addition, since nm-sized ultra-fine particles have a verysensitive surf ace as described above, it may become necessary to form aquantum dot functional structure having the particles beinghomogeneously distributed in a stable transparent medium.

[0021] In addition, in order to obtain fine particles having a specifiedparticle diameter, a fine particle classifier may be used forclassifying the diameter of fine particles using the mobility which isdependent on the particle diameter. Such a fine particle classifier hasbeen used for performance test of high-performance air filters forcollecting and separating sub-micron fine particles with highefficiency, and for generating standard fine particles and measuring theparticle diameter upon monitoring of cleaned atmosphere. The mobilityemployed for classifying the diameter of particles includes mainly theelectrical mobility of charged particles in an electro-static field andthe dynamic mobility caused by gravitational force. In addition, theaforementioned fine particle classifier has two main structures: adouble cylinder and a disk type structure.

[0022]FIG. 3 is a schematic view illustrating the structure of aprior-art differential electrical mobility classifier, introduced inJapanese Journal of Aerosol Research Vol.2, No.2, p106 (1987) or inJapanese Journal of Powder Engineering Society Vol.21, No.12, p753(1984). This differential electrical mobility classifier has a doublecylindrical structure comprising an outer cylinder (of radius R1) 19 andan inner cylinder (of radius R2) 20 disposed inside the outer cylinder19 concentrically with the outer cylinder 19. Referring to FIG. 3,charged fine particles 21 are transported by a carrier gas 22 to flowinto the double cylinder classifier from the upper and portion thereofto be mixed with clean air or a sheath gas 23 flowing therein. Themixture gas of the charged fine particles 21 and the sheath gas 23 flowsas a laminar flow over a length of L through the double cylinderportion. An electrostatic field is applied to this double cylinderportion with a direct current power supply 24 in a directionperpendicular to the flow of said mixture gas. This causes the chargedfine particles 21 to draw an orbit in accordance with the electricalmobility of each particle. Since said electrical mobility is dependenton the diameter of fine particles, only those fine particles having aspecific diameter arrive at a lower slit 25 and then are classified tobe taken out of a carrier gas exhaust vent 26. The fine particles ofother diameters are exhausted from a sheath gas exhaust vent 27 inconjunction with the sheath gas 23 or caused to move to and adhere to aninner collector electrode 28.

[0023] On the other hand, as a prior art fine particle classifier, adynamic mobility classifier having a disk structure is disclosed inJapanese Patent Disclosure No. 9-269288. FIG. 4 is a schematic viewillustrating the structure of the dynamic mobility classifier of theaforementioned disk type.

[0024] This disk-type dynamic mobility classifier comprises adisk-shaped upper disk 31, a disk-shaped lower disk 32 disposed oppositeto and spaced apart by a predetermined distance from the upper disk 31,and a particle collector portion 33 attached to the lower disk 32 anddisposed opposite to the upper disk 31. There is formed a cylindricalcentral suction duct 34, having an opening at one end thereof, on thecentral portion of the upper disk 31. There are formed a plurality ofholes or slits 35 for introducing a carrier gas in the vicinity of therim portion of the disk in the outward radial direction from the centralsuction duct 34. The lower disk 32 is provided with substantially thesame diameter as that of the upper disk 31 and disposed generally inconcentric relationship therewith. There are formed a plurality of holesor slits 36 for emitting a carrier gas on a portion apart by apredetermined distance in the outward radial direction from the centerof the lower disk 32. The slits 35 provided on the upper disk 31 and theslits 36 provided on the lower disk 32 are a plurality of slits formedin an annular shape along a predetermined circumference, spaced apart atcertain intervals. The distance radially outward from the center of thedisk to the position of the slits 36 provided on the lower disk 32 isdesigned to be less than the distance radially outward from the centerof the disk to the slits 35 provided on the upper disk 31. Between theupper disc 31 and the lower disk 32, there is defined a space or aclassifying region 37. On the central portion of the particle collectorportion 33, there is formed a cylindrical withdrawal duct 38 having anopening at one end thereof. The particle collector portion 33 is adaptedto discharge classified fine particles from the withdrawal duct 38 inconjunction with the carrier gas.

[0025] Referring to FIG. 4, the classifying region 37 is formed in aspace defined between the upper disk 31 and the lower disk 32, arrangedto be concentric and parallel to each other. A sheath gas or an air flow39 is introduced into the classifying region 37 from the periphery ofthe upper and lower disks 31, 32, being supplied from the outer riminwardly in the radial direction. The air flow 39 takes place as acentripetal laminar flow through the classifying region 37 and isexhausted from the central suction duct 34 (indicated by arrow A1 inFIG. 4). Fine particles 40 are transported with a carrier gas 41 to beguided from the slits 35 provided on the upper disk 31 into theclassifying region 37. The fine particles 40, which have been guidedfrom the slits 35 provided on the upper disk 31 into the classifyingregion 37, are moved with the air flow 39 toward the center axis as wellas drop from the upper disk 31 toward the lower disk 32 due to thegravitational field. Since the drop speed is dependent on the diameterof the fine particles 40, only those fine particles having a certaindiameter are allowed to reach the slits 36 arranged on the lower disk32, thus being classified and taken out of the withdrawal duct 38(indicated by arrow A2 in FIG. 4). The particles having other diametersare exhausted from the central suction duct 34 in conjunction with theair flow or moved to the lower disk 32 to adhere to the surface thereof.

[0026] In the field of such fine particle classification technology,known is that the physical properties of ultra-fine particles havingdiameters from a few to a few tens of nanometers vary depending on theparticle diameter. For example, the energy gap of semiconductorultra-fine particles increases as the particle diameter decreases.Attempts have been made to create new devices by making use of thephysical properties of the aforementioned semiconductor ultra-fineparticles. As a substance for forming the aforementioned new device, Sihas received attention. In this context, attempts have been made tocreate ultra-fine particles of Si having diameters from a few to a fewtens of nanometers by making use of the pulse laser ablation in a raregas. To create a new device employing the Si ultra-fine particles, it isnecessary to classify the Si ultra-fine particles having variousdiameters on the order of a few to a few tens of nanometers and thusextract those Si ultra-fine particles having a narrow particle diameterdistribution enough to regard the particles as having a single diameter.In addition, the mean particle diameter of the Si ultra-fine particlesto be classified can be preferably varied.

[0027] On the other hand, the prior art disk type dynamic mobilityclassifier shown in FIG. 4 is adapted to classify fine particles havinggenerally sub-micron diameters, employing the gravitational field forclassifying the particle diameter. Since the gravitational field isconstant, it is necessary to vary the flow rate of the air flow 39 inorder to vary the mean particle diameter of the ultra-fine particlesbeing classified. A variation in mean particle diameter of nm-sizedultra-fine particles requires a fine variation in flow rate of theaforementioned air flow 39. It is extremely difficult to control thisfine variation in flow rate and to stabilize the flow rate.

[0028] Furthermore, in order to classify ultra-fine particles havingsub-micron or less diameters without increasing the size of theaforementioned disk type dynamic mobility classifier (i.e., withoutincreasing the projective distance of the annually formed slits 35, 36),it is necessary to apply a force greater in magnitude than thegravitational force to the ultra-fine particles in a directionperpendicular to a sheath gas flow or the air flow 39 (in the directionfrom the upper disk 31 to the lower disk 32) in the classifying region37.

[0029] In addition, as a method for improving the classificationresolution of the ultra-fine particles, such a technique is availablethat increases the classifying region from one stage to multiple stagesto increase the number of times of classification. Referring to thedouble cylinder classifier shown in FIG. 3, for example, the doublecylinder classifier described in the Japanese Journal of PowderEngineering Society Vol.21, No.12, p753 (1984) has the dimensions of theclassifying region of L=400 mm, R2=15 mm, and R1=25 mm. In this context,suppose a cylindrical classifying region is further added to the outerperiphery of the aforementioned double cylinder classifier to providemultiple stages of the classifying region. In this case, the overalldimensions of the classifier would be significantly increased.Therefore, it is necessary to employ a structure other than that of thedouble cylinder type to make the overall dimensions of the classifiersmall.

SUMMARY OF THE INVENTION

[0030] In order to solve the aforementioned prior art problems, theapparatus for fabricating a quantum dot functional structure accordingto the present invention is constructed as follows. That is, theapparatus comprises a fine particle generating chamber for generatingultra-fine particles by laser ablation and a fine particle classifyingchamber for classifying the ultra-fine particles according to theirparticle diameters. The apparatus also comprises a transparent mediumgenerating chamber for generating a transparent medium by laser ablationand a depositing chamber for depositing the ultra-fine particles onto asubstrate and embedding the particles in the transparent medium at thesame time.

[0031] With this apparatus, it is made possible to efficiently fabricatehigh-purity ultra-fine particles having a single particle diameter anduniform structure with their contamination and damage being alleviated.It is also made possible to deposit the particles onto the substrate inconjunction with the transparent medium and thus fabricate an opticallyfunctioning device employing, as an active layer, a quantum dotfunctional structure having the ultra-fine particles homogeneouslydistributed in the transparent medium.

[0032] As various embodiments according to the present inventionconfigured as described above, the present invention provides anapparatus for fabricating a quantum dot functional structurecharacterized by being constructed as follows. That is, the apparatuscomprises a fine particle generating chamber for generating fineparticles and a fins particle classifying chamber for classifying fineparticle generated in the fine particle generating chamber according toa desired particle diameter in a gas. The apparatus also comprises gasexhaust means for exhausting a ads for transporting the fine particlesand transparent medium generating means for generating a transparentmedium. The apparatus further comprises a depositing chamber forcollecting fine particles classified in the fine particle classifyingchamber onto a substrate as well as for collecting a transparent mediumgenerated by the transparent medium generating means onto the substrateand for depositing the classified fine particles and the transparentmedium onto the substrate. This makes it possible to efficientlyfabricate high-purity ultra-fine particles having a single particlediameter and uniform structure with their contamination and damage beingalleviated. It is also made possible to deposit the particles onto thesubstrate in conjunction with the transparent medium at the same timeand thus fabricate an optically functioning device employing, as anactive layer, a quantum dot functional structure having the ultra-fineparticles homogeneously distributed in the transparent medium.

[0033] The present invention also provides an apparatus for fabricatinga quantum dot functional structure, characterized by further comprisingfirst transparent medium generating means arranged in the depositingchamber, and a second independent transparent medium generating chamberas the transparent medium generating means. For example, this canprevent fine particles of a material susceptible to oxidation from beingoxidized when such a material is used as the transparent medium that canmake the atmosphere near the deposition substrate oxidative upongeneration of the transparent medium. Thus, the present invention canextend the range of selection of materials for fabricating a quantum dotfunctional structure.

[0034] The present invention also provides an apparatus for fabricatinga quantum dot functional structure, characterized in that the fineparticle generating chamber, the fine particle classifying chamber, anda transport path of fine particles in the depositing chamber areconstructed on a straight line. Thus, the apparatus can prevent theexhaust conductance of a transport path from being reduced upontransportation of ultra-fine particles in a gas and the ultra-fineparticles from being deposited in the transport path upon transportationof the particles, thereby leading to an improvement in yield of theparticles.

[0035] The present invention also provides an apparatus for fabricatinga quantum dot functional structure, characterized in that the pressureof the fine particle generating chamber and the pressure of thedepositing chamber are controlled independently. Thus, the apparatus cancontrol with accuracy the pressure for generating the ultra-fineparticles and the transparent medium at the optimum value for eachmaterial, thereby making it possible to control with accuracy thestructure and physical properties of the quantum dot functionalstructure.

[0036] The present invention also provides an apparatus for fabricatinga quantum dot functional structure, characterized in that the gasexhaust means is controlled in accordance with the pressure of thedepositing chamber. This makes it possible to provide a largerdifference in pressure between the fine particle generating chamber andthe depositing chamber, thereby improving the transport efficiency ofthe ultra-fine particles.

[0037] The present invention also provides an apparatus for fabricatinga quantum dot functional structure, characterized in that the substratein the depositing chamber is rotatable with respect to a direction ofdeposition of the fine particles and transparent medium. This makes itpossible to improve the deposition efficiency when the ultra-fineparticles and the transparent medium are alternately deposited.

[0038] The present invention also provides an apparatus for fabricatinga quantum dot functional structure, characterized by further comprisinga temperature control mechanism being capable of maintaining a transportpath of fine particles at a constant temperature. This can prevent theultra-fine particles from being deposited in the transport pipe bythermo-phoresis effect, also preventing the mutual cohesion of theultra-fine particles.

[0039] The present invention also provides an apparatus for fabricatinga quantum dot functional structure, characterized in that at least oneof the fine particles and the transparent medium is generated usinglaser ablation, and a plasma plume produced upon generation is observedusing a charge coupled device. The apparatus allows the laser ablationto be observed in real time, thereby making it possible to determine thestability of the laser ablation upon generation of the ultra-fineparticles and transparent medium.

[0040] The present invention also provides an apparatus for fabricatinga quantum dot functional structure, characterized in that at least oneof the generated fine particles and the transparent medium is radiatedwith ultraviolet light to observe fluorescent light. The apparatusallows for observing in real time the process of generating theultra-fine particles and the transparent medium, making it possible toefficiently capture the ultra-fine particles into the fine particleclassifying chamber as well as efficiently deposit the transparentmedium.

[0041] The present invention also provides a quantum dot functionalstructure fabricated by the aforementioned apparatus for fabricating aquantum dot functional structure. Thus, it is made possible to realizean optically functioning device employing an active layer with astructure having the ultra-fine particles homogeneously distributed in astable transparent medium.

[0042] The present invention also provides am optically functioningdevice employing the aforementioned quantum dot functional structure asan active layer, thereby making it possible to improve the efficiencywhen compared with that of the prior art.

[0043] The present invention also provides a method for fabricating aquantum dot functional structure, characterized by comprising the stepsof generating fine particles; classifying the fine particles generatedaccording to a desired particle diameter in a gas; exhausting a gas fortransporting the fine particles after the classifying step; collectingthe classified fine particles onto a substrate and generating atransparent medium at the same time; and depositing the classified fineparticles and the transparent medium onto the substrate at the sametime. The method makes it possible to efficiently fabricate high-purityultra-fine particles having a single particle diameter and uniformstructure with their contamination and damage being alleviated. It isalso made possible to deposit the particles onto the substrate inconjunction with the transparent medium at the same time and thusfabricate an optically functioning device employing, as an active layer,a quantum dot functional structure having the ultra-fine particleshomogeneously distributed in the transparent medium.

[0044] The present Invention also provides a method for fabricating aquantum dot functional structure, characterized in that the transparentmedium is generated using, at the same time or alternately, any one ofor both first transparent medium generating means, disposed in adepositing chamber for depositing the fine particles and the transparentmedium, and second transparent medium generating means arrangedindependently. For example, this can prevent fine particles of amaterial susceptible to oxidation from being oxidized when such amaterial is used as the transparent medium that can make the atmospherenear the deposition substrate oxidative upon generation of thetransparent medium. Thus, the present invention can extend the range ofselection of materials for fabricating a quantum dot functionalstructure.

[0045] The present invention also provides a method for fabricating aquantum dot functional structure, characterized in that the fineparticles and the transparent medium are controlled independently ofeach other so that each pressure upon generation thereof becomes optimumat the same time, and thereby generated. Thus, the method can controlwith accuracy the pressure for generating the ultra-fine particles andthe transparent medium at the optimum value for each material, therebymaking it possible to control with accuracy the structure and physicalproperties of the quantum dot functional structure.

[0046] The present invention also provides a method for fabricating aquantum dot functional structure, characterized in that the gas fortransporting fine particles is exhausted, after the step of classifyingthe fine particles, in accordance with a pressure of the depositingchamber for depositing the fine particles and the transparent mediumonto the substrate. This makes it possible to provide a largerdifference in pressure between the fine particle generating chamber andthe depositing chamber, thereby improving the transport efficiency ofthe ultra-fine particles.

[0047] The present invention also provides a method for fabricating aquantum dot functional structure, characterized by further comprisingthe step of maintaining a path of the fine particles at a constanttemperature after the step of classifying the fine particles. This canprevent the ultra-fine particles from being deposited in the transportpipe by thermo-phoresis effect, also preventing the mutual cohesion ofthe ultra-fine particles.

[0048] The present invention also provides a method for fabricating aquantum dot functional structure, characterized by further comprisingthe step of observing, using a charge coupled device, a plasma plumeproduced when at least one of the fine particles and the transparentmedium is generated using laser ablation. The method allows the laserablation to be observed in real time, thereby making it possible todetermine the stability of the laser ablation upon generation of theultra-fine particles and transparent medium.

[0049] The present invention also provides a method for fabricating aquantum dot functional structure, characterized by further comprisingthe step of observing fluorescent light from the fine particles and thetransparent medium, emitted when at least one of the fine particles andthe transparent medium is radiated with ultraviolet light upongeneration thereof. Thus, it is made possible to observe in real timethe process of generating the ultra-fine particles, leading to animproved deposition efficiency.

[0050] The present invention also provides a quantum dot functionalstructure fabricated by the aforementioned method for fabricating aquantum dot functional structure. Thus, it is made possible to realizean optically functioning device employing an active layer with astructure having the ultra-fine particles homogeneously distributed in astable transparent medium.

[0051] The present Invention also provides an optically functioningdevice employing the aforementioned quantum dot functional structure asan active layer, thereby making it possible to improve the efficiencywhen compared with that of the prior art.

[0052] As described above, according to the present invention, nm-sizedhigh-purity ultra-fine particles having a single diameter and uniformstructure can be fabricated efficiently with their contamination anddamage being alleviated and deposited on a deposition substrate. Inaddition, it is also made possible to fabricate an optically functioningdevice which employs as the active layer the quantum dot functionalstructure having the ultra-fine particles distributed homogeneously inthe stable transparent medium.

[0053] Furthermore, as an improvement of a disk type dynamic mobilityclassifier that can be incorporated into the apparatus for fabricating aquantum dot functional structure, the present invention allows a directcurrent voltage to be applied between the upper and lower disks. Thismakes it possible to establish an electrostatic field in the verticaldirection in a classifying region (in a direction perpendicular to anair flow). Thus, when fine particles are charged which are introducedinto the aforementioned disk type dynamic mobility classifier, it ismade possible to classify the charged fine particles not according tothe dynamic mobility caused by the gravitational field but according tothe electrical mobility caused by the electrostatic field. Increasingthe direct current voltage applied between the upper and lower disksmakes it possible to produce an electrostatic force that is greater thanthe gravitational force. This makes it possible to classify nm-sizedultra-fine particles without increasing the aforementioned disk typedynamic mobility classifier in size (without increasing the annularguide slits and the projection distance of the annular slits).

[0054] Furthermore, varying the direct current voltage applied betweenthe upper and lower disks makes it possible to change the strength ofthe electrostatic field with accuracy. Thus, this also makes it possibleto vary the mean particle diameter upon classification of nm-sizedcharged ultra-fine particles at a constant flow rate of air.

[0055] Furthermore, in the aforementioned disk type dynamic mobilityclassifier, the classifying region is constituted by multiple stagesinstead of one stage. This makes it possible to reduce the size of theoverall classifier and improve the classifying resolution of nm-sizedcharged ultra-fine particles. More specifically, a third disk isarranged on the lower portion of the lower disk of the aforementioneddisk type dynamic mobility classifier, concentrically in parallelthereto. A space between the lower disk and the third disk is employedas a second stage classifying region. In the same manner as this, afourth disk, a fifth disk, . . . are arranged to define a third stageclassifying region, a fourth stage classifying region, . . . .

[0056] As described above, according to the present invention, a disktype dynamic mobility classifier is implemented in which a directcurrent voltage can be applied between upper and lower disks and whichis provided with a multi-stage classifying region, thereby providing adisk type ultra-fine particle classifier for classifying nm-sizedultra-fine particles with good resolution.

[0057] Accordingly, it is a first object of the present invention toprovide an apparatus for fabricating a quantum dot functional structure,in which nm-sized high-purity ultra-fine particles having a singlediameter and uniform structure can be fabricated efficiently with theircontamination and damage being alleviated and deposited on, a depositionsubstrate. In addition, the apparatus makes it possible to fabricate anoptically functioning device which employs as the active layer thequantum dot functional structure having the ultra-fine particlesdistributed homogeneously in the stable transparent medium.

[0058] In addition, it is a second object of the present invention toprovide an ultra-fine particle classifier which can classify nm-sizedultra-fine particles with good resolution.

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] These objects and advantages of the present invention will becomeclear from the following description on the embodiments with referenceto the accompanying drawings, wherein:

[0060]FIG. 1 is a conceptual view illustrating a prior art apparatus forfabricating and depositing ultra-fine particles;

[0061]FIG. 2 is a graph illustrating the absorption edge emission energybeing increased due to the quantum confinement affect with decreasingdiameter of the ultra-fine particles;

[0062]FIG. 3 is a schematic view illustrating the structure of a priorart differential electrical mobility classifier of a double cylinderstructure;

[0063]FIG. 4 is a schematic view illustrating the structure of a priorart disk type dynamic mobility classifier;

[0064]FIG. 5 is a view illustrating the overall configuration of aquantum dot functional structure fabricating apparatus according to anembodiment of the present invention;

[0065]FIG. 6 is a sectional view illustrating the configuration of anultra-fine particle generating chamber according to an embodiment of thepresent invention;

[0066]FIG. 7 is a sectional view illustrating the configuration of anultra-fine particle classifying chamber according to an embodiment ofthe present invention;

[0067]FIG. 8 is a sectional view illustrating the configuration of adepositing chamber and a transparent medium generating chamber accordingto an embodiment of the present invention;

[0068]FIG. 9 is a sectional view illustrating the configuration of aquantum dot functional structure according to an embodiment of thepresent invention;

[0069]FIG. 10 is a sectional view illustrating a charging chamberaccording to an embodiment of the present invention;

[0070]FIG. 11 is a view illustrating the configuration of anotherexample of a holder and depositing substrate, which are used in adepositing chamber according to an embodiment of the present invention;

[0071]FIG. 12 is a schematic view illustrating the configuration of animproved disk type ultra-fine particle classifier, which can be employedfor fabricating a quantum dot functional structure according to a secondembodiment of the present invention; and

[0072] FIGS. 13(a) and 13(b) are schematic graphs illustrating therelationship between the number and diameter of the ultra-fine particlesclassified in each classifying region of the disk type ultra-fineparticle classifier shown in FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0073] (First Embodiment)

[0074] Now, an apparatus for fabricating a quantum dot functionalstructure according to a first embodiment of the present invention willbe explained in detail with reference to FIGS. 5 to 11.

[0075]FIG. 5 is a view illustrating the overall configuration of anapparatus for fabricating a quantum dot functional structure accordingto this embodiment. The apparatus for fabricating a quantum dotfunctional structure according to this embodiment principally comprisesan ultra-fine particle generating chamber 101 for generating ultra-fineparticles, an ultra-fine particle classifying chamber 102, a depositingchamber 103, and a transparent medium generating chamber 104 forgenerating a transparent medium. Here, the ultra-fine particleclassifying chamber 102 is coupled to the ultra-fine particle generatingchamber 101 to classify the ultra-fine particles generated in theultra-fine particle generating chamber 101. The depositing chamber 103is further coupled to the ultra-fine particle classifying chamber 102 toallow the ultra-fine particles classified in the ultra-fine particleclassifying chamber 102 to be deposited.

[0076]FIG. 6 is a sectional view illustrating the configuration of theultra-fine particle generating chamber 101. As shown in FIG. 6, theultra-fine particle generating chamber 101 is configured to haveprincipally a gas guide line 213 and a self-rotating mechanism 215.Here, the gas guide line 213 introduces a carrier gas 202 (e.g., He gasof a purity of 99.9999%) into the ultra-fine particle generating chamber101 through a mass flow controller 201 at a constant mass flow rate Qa(e.g., 1.0 (liter/minute)) via gas ejecting openings 214 disposed In anannular form. The self-rotating mechanism 215 is provided with a targetholder 206 for fixedly holding a semiconductor target 207 (e.g., asingle crystal Si water of surface orientation (100), diameter 50 mm,and thickness 0.625 mm). In addition, the ultra-fine particle generatingchamber 101 comprises a condensing lens 203 and a laser lightillumination assembly 216 provided with a laser light inlet window 204.The condensing lens 203 is arranged at an angle of 45 degrees relativeto the transport path of ultra-fine particles to condense pulsed laserlight (e.g., the second-order harmonic of the Nd-YGA laser of wavelength532 nm) 205. The laser light inlet window 204 introduces the laser lightcondensed by the condensing lens 203 into the ultra-fine particlegenerating chamber 101 to radiate the semiconductor target 207 fixed onthe target holder 206 with the aforementioned pulsed laser light. Theultra-fine particle generating chamber 101 comprises an ultra-fineparticle intake pipe 209 extending in the same transport direction asthat of growth of the ultra-fine particles of an ablation plume 208excited by the pulsed laser light 205. The chamber 101 also comprises apair of viewing windows 210, 211 for allowing real-time observation ofthe ablation plume 208, etc., and an ultra-high vacuum exhaust system212 mainly comprising a turbo molecular pump for pumping the ultra-fineparticle; generating chamber 101 down to an ultra-high vacuum less than1×10⁻⁹ Torr prior to the fabrication of an optically functioning device.The ultra-fine particles generated by the excitation of the pulsed laserlight 205 are fed out of the ultra-fine particle generating chamber 101through the ultra-fine particle intake pipe 209.

[0077]FIG. 7 is a sectional view illustrating the configuration of theultra-fine particle classifying chamber 102. As shown in FIG. 7, theultra-fine particle classifying chamber 102 comprises principally acharging chamber 301 coupled to the ultra-fine particle generatingchamber 101 to intake and charge the ultra-fine particles generated inthe ultra-fine particle generating chamber 101. The chamber 102 alsocomprises an ultra-fine particle inlet pipe 302 for guiding theultra-fine particles from the ultra-fins particle generating chamber 101and a differential electrical mobility classifier 303, employed as aclassifier, for classifying the ultra-fine particles fed from theultra-fine particle inlet pipe 302. The chamber 102 further comprises amass flow controller 305 for introducing a sheath gas 304 into thedifferential electrical mobility classifier 303 and a direct currentpower supply 306 for forming an electrostatic field between the doublecylinders of the differential electrical mobility classifier 303. Thechamber 102 still further comprises a sheath gas exhaust system 308 forexhausting a sheath gas and a carrier gas exhaust system 309 forexhausting part of the carrier gas 202 in conjunction with theclassified ultra-fine particles classified in the differentialelectrical mobility classifier 303.

[0078] The charging chamber 301 charges the ultra-fine particles, whichare generated in the ultra-fine particle generating chamber 101 andtransported at a flow rate of Qa, with a vacuum ultraviolet light sourcesuch as an excimer lamp (an Ar2 excimer of wavelength 126 nm). Theultra-fine particles can be charged using a radioactive isotope such asamericium 241 (Am 241) or both the vacuum ultraviolet light source andthe radioactive isotope at the same time. The ultra-fine particle inletpipe 302 is arranged generally in a straight line from the ultra-fineparticle generating chamber 101 toward the depositing chamber 103 andbranched on the way, for example, into four equal parts. In thisembodiment, the differential electrical mobility classifier 303 has adouble cylinder structure for receiving charged ultra-fine particlesfrom the ultra-fine particle inlet pipe 302 to classify the ultra-fineparticles according to the desired diameter. The mass flow controller305 controllably introduces the sheath gas 304 (e.g., a He gas of apurity of 99.9999%) into the differential electrical mobility classifier303 to form a flow of a constant mass flow rate Qc (e.g., 5l/min) insidethe differential electrical mobility classifier 303. The sheath gasexhaust system 308 is controlled by means of a mass flow meter 307disposed at the front stage of a pump via an exhaust pipe of highconductance to exhaust the sheath gas with a helical pump or the like atthe constant mass flow rate Qc. The carrier gas exhaust system 309exhausts only part of the carrier gas 202 flowing at the mass flow rateQa in conjunction with the classified ultra-fine particles classifiedwith the differential electrical mobility classifier 303 using pumpsmainly by means of the turbo molecular pump. In addition, the carriergas exhaust system 309 is controlled inn accordance with the pressure ofthe depositing chamber, described later.

[0079]FIG. 8 is a sectional view illustrating the configuration of thedepositing chamber 103. As shown In FIG. 8, the depositing chamber 103comprises principally an ultra-fine particle depositing nozzle 401 forejecting an in-coming carrier gas containing classified ultra-fineparticles and a depositing substrate holder 404. The chamber 103 alsocomprises a depositing substrate 405 fixed to the depositing substrateholder 404, and a laser illumination system 430 constituted by acondensing lens 406 and a laser light inlet window 407. The chamber 103further comprises a target holder 409 and a transparent medium target411 arranged therein, and an ultra-high vacuum exhaust system 412 forpumping the depositing chamber 103 down to an ultra-high vacuum. Thechamber 103 still further comprises a depositing chamber gas exhaustsystem 413 for exhausting differentially the carrier gas in thedepositing chamber 103, a micro-ammeter 414 for measuring the exchangeof electrons between the ultra-fine particles and the depositingsubstrate 405 in the depositing chamber 103, and a transparent mediumdepositing nozzle 415 for ejecting the transparent medium transportedfrom the transparent medium generating chamber 104.

[0080] The ultra-fine particles generated in the ultra-fine particlegenerating chamber 101 are classified into those of a single particlediameter in the ultra-fine particle classifying chamber 102 andthereafter the ultra-fine particle depositing nozzle 401 ejects theincoming carrier gas containing the classified ultra-fine particles. Theultra-fine particle depositing nozzle 401 is coupled with a heater 402for maintaining the ultra-fine particle depositing nozzle at a constanttemperature and a controller 403 for controlling the operation of theheater 402. The laser illumination system 430 allows excimer laser light408 to be condensed through the condensing lens 406 and introduced intothe depositing chamber 103 via the laser light inlet window 407. Thetarget holder 409 fixes the target 411 excited by the excimer laserlight 408 as well as drivingly rotates the target 411 at a constantspeed (e.g., at 8 rpm).

[0081] In this embodiment, the target 411 is formed, for example, of thetransparent medium target 411 (e.g., a sintered target of In₂O₃ having apurity of 99.99%, a diameter of 50 mm, and a thickness of 3 mm).Moreover, on the target holder 409, the target 411 is arranged inparallel to the depositing substrate 405 so as to direct the directionof growth of an ablation plume 410 excitedly irradiated with the excimerlaser light 408 toward the depositing substrate 405. On the depositingsubstrate 405, deposited are the ultra-fine particles generated from thetarget 411 radiated with the excimer laser light 408 and the transparentmedium transported from the transparent medium generating chamber 104.The ultra-high vacuum exhaust system 412 comprises mainly a turbomolecular pump for pumping the depositing chamber 103 down to aultra-high vacuum less than 1×10⁻⁹ Torr prior to the fabrication of aquantum dot functional structure. The depositing chamber gas exhaustsystem 413 mainly comprises a helical pump for exhausting differentiallya carrier gas so as to maintain the ultra-fine particle generatingchamber 101 at a constant pressure (e.g., 4.0 Torr). The micro-ammeter414 measures as an electric current the electrons to be exchanged whenthe charged ultra-fine particles classified in the depositing chamber103 are deposited on the depositing substrate 405.

[0082] On the other hand, as shown in FIG. 8, the transparent mediumgenerating chamber 104 principally comprises a gas guide system 431 forintroducing an atmospheric rare gas 417 into the transparent mediumgenerating chamber 104 and a laser illumination system 432 constitutedby a condensing lens 418 and a laser light inlet window 419. The chamber104 also comprises a target holder 421 and a transparent medium target422 arranged thereon, a transparent medium intake pipe 424, and a pairof viewing windows 425, 426 for allowing real-time observation of anablation plume 423 or the like excited by excimer laser light 420.

[0083] The gas guide system 431 introduces the atmospheric rare gas 417(e.g., a He gas of a purity of 99.9999%) into the transparent mediumgenerating chamber 104 at a constant mass flow rate QT (e.g.,0.5[l/min]) via a mass flow controller 416. The target holder 421 fixesthe target 422 excited by the excimer laser light 420 as well asdrivingly rotates the target 422 at a constant speed (e.g., at 8 rpm).In this embodiment, the target 422 is formed, for example, of atransparent medium target (e.g., a sintered target of In₂O₃ having apurity of 99.99%, a diameter of 50 mm, and a thickness of 3 mm).Moreover, on the target holder 421, the transparent medium target 422 isarranged in parallel to the depositing substrate 405 so as to direct thedirection of growth of the ablation plume 410 excitedly irradiated withthe excimer laser light 408 toward the depositing substrate 405. Thetransparent medium intake pipe 424 is arranged toward the direction ofgrowth of the ablation plume 423 excited by the excimer laser light 420.

[0084]FIG. 9 is a sectional view illustrating the configuration of thequantum dot functional structure according to this embodiment. Withreference to FIGS. 6 to 11, explanations will be given the fabricationof the quantum dot functional structure, as shown in FIG. 9, with asectional structure where high-purity ultra-fine particles 501 of asingle diameter and uniform structure are homogeneously distributed in atransparent medium 502. First, to eliminate the effect of damage,contamination or the like prior to fabricating the quantum dotfunctional structure, a valve 310 of FIG. 7 is closed to allow theultra-high vacuum exhaust system 212 of FIGS. 6, comprising mainly theturbo molecular pump, to pump the ultra-fine particle generating chamber101 down to an ultra-high vacuum less than 1×10⁻⁹ Torr, and thereafterthe ultra-high vacuum exhaust system 212 is closed.

[0085] At the same time, the ultra-high vacuum exhaust system 412 ofFIG. 8, comprising mainly the turbo molecular pump, is allowed to pumpthe ultra-fine particle classifying chamber 102, the depositing chamber103, and the transparent medium generating chamber 104 down to anultra-high vacuum less than 1×10⁻⁹ Torr, and thereafter the ultra-highvacuum exhaust system 412 is closed.

[0086] Subsequently, the mass flow controller 201 of FIG. 6 is used tointroduce the carrier gas 202 (a high purity rare gas, e.g., a He gas ofa purity of 99.9999%) at the mass flow rate Qa (0.5[l/min] in this case)into the ultra-fine particle generating chamber 101.

[0087] Then, the valves 310, 311 of FIG. 7 are opened to control thedepositing chamber gas exhaust system 413 of FIG. 8, mainly constitutedby the helical pump, with reference to the pressure of the ultra-fineparticle generating chamber 101, and differential exhaust is performedto maintain the ultra-fine particle generating chamber 101 at a constantpressure P1 (e.g., 10 Torr).

[0088] Here, the surface of the semiconductor target 207 is excited withthee condensed pulsed laser light 205 of FIG. 6 to produce the ablationreaction so as to completely remove the natural oxide film formed on thesurface of the semiconductor target 207 and Impurities such as metallicor carbon compounds adhered to the surface of the target. Thereafter,the depositing chamber gas exhaust system 413 of FIG. 8 is closed. Atthis point, the lasing of the pulsed laser light 205 is at a standstill.

[0089] As described above, the natural oxide film is removed which isformed on the surface of the semiconductor target 207. It is therebymade possible to eliminate the effect exerted by the oxide film, whichmay contaminate and is an impurity for the semiconductor ultra-fineparticle, and the metallic or carbon compounds adhered to the surface ofthe target or the like.

[0090] Then, the carrier gas 202 is changed in its flow rate andintroduced at a constant mass glow rate Qa (1.0[l/min] under standardcondition). At the same time, the mass flow controller 305 of FIG. 7 isused to introduce the sheath gas 304 (a high purity rare gas, e.g., a Hegas of a purity of 99.9999%) at the mass flow rate Qc (0.5[l/min] understandard condition) into the differential electrical mobility classifier303.

[0091] Here, the depositing chamber gas exhaust system 413 mainlyconstituted by the helical pump is opened to exhaust differentially thecarrier gas so as to maintain the ultra-fine particle generating chamber101 at a constant pressure P1 (e.g., 5.0 Torr). At the same time, thesheath gas exhaust system 308, mainly constituted by the helical pumpand provided for the ultra-fine particle classifying chamber 102, isopened to control the sheath gas exhaust system 308 with reference tothe reading of the mass flow meter 307 so as to allow the mass flowmeter 307 to read 5.0 [l/min], thereby exhausting the sheath gas at aconstant mass flow rate Qc.

[0092] Furthermore, a valve 312 in opened at the same time to exhaustdifferentially only part of the carrier gas so as to maintain thedepositing chamber 103 at a constant pressure P2 (e.g., 2.0 Torr) usingthe carrier gas exhaust system 309 controlled with reference to thepressure of the depositing chamber 103. At this point, the sum of themass flow rate of the gases exhausted through the depositing chamber gasexhaust system 413 and the carrier gas exhaust system 309 is 1.0[l/min], while the ultra-fine particle generating chamber is kept at aconstant pressure P1 (5.0 Torr) and the depositing chamber is kept at aconstant pressure P2 (2.0 Torr).

[0093] Exhaustion of gases by the aforementioned means can control thepressure of the ultra-fine particle generating chamber 101 at P1, thepressure of the depositing chamber at P2, and the exhaust mass flow rateof the sheath gas at Qc with accuracy.

[0094] Then, the pulsed laser light 205 is lased to be introduced intothe ultra-fine particle generating chamber 101. At this time, in theultra-fine particle generating chamber 101, the substance detached andejected due to the ablation reaction from the semiconductor target 207excited by the pulsed laser light 205 dissipates its kinetic energy intothe atmospheric rare gas molecules, thereby urging the condensation andgrowth of the substance in the gas and thus allowing the substance togrow to ultra-fine particles of a few to a few tens of nanometers.

[0095] Here, controlling and maintaining the ultra-fine particlegenerating chamber at a constant pressure P1 with accuracy by theaforementioned means mares it possible to allow the semiconductorultra-fine particles to condense and grow under the optimum condition

[0096]FIG. 10 is a sectional, view illustrating the configuration of thecharging chamber 301 according to an embodiment of the presentinvention. This charging chamber 301 comprises a vacuum ultravioletlight source 351 for generating and emitting ultraviolet light, and anoptical system 353 for condensing vacuum ultraviolet light 352 emittedfrom the vacuum ultraviolet light source 351 and for radiating thecharging chamber 301 with the light. The high-purity semiconductorultra-fine particles generated in the ultra-fine particle generatingchamber 101 are transported to the charging chamber 301, configured asshown in FIG. 10, via the ultra-fine particle intake pipe 209 inconjunction with a carrier gas flowing at a constant mass flow rate Qa.The high-purity semiconductor ultra-fine particles transported to thecharging chamber 301 are charged to have a single polarity with thevacuum ultraviolet light 352 emitted from the vacuum ultraviolet lightsource 351 and formed through the optical system 353.

[0097] The high-purity semiconductor ultra-fine particles charged tohave a single polarity in the charging chamber 301 flow into thedifferential electrical mobility classifier 303 via the ultra-fineparticle inlet pipe 302, which is arranged at four equal intervalsspaced by 90 degrees. The high-purity semiconductor ultra-fine particlesthat have flown into the differential electrical mobility classifier 303of the double cylinder type are classified according to the desiredsingle diameter (e.g., a particle diameter of 3.7 nm) through theelectrostatic field established between the inner and outer cylinderswith the direct current power supply 306 (e.g., at a voltage of 2.5V).

[0098] Here, the mass flow rate of the carrier and sheath gases to beintroduced through the aforementioned means and the mass flow rate ofthe carrier and sheath gases to be exhausted are controlled so as to beequal to eat other, respectively, thereby allowing the classificationaccuracy of the differential electrical mobility classifier 303 toapproach a theoretical value.

[0099] Then, the high-purity semiconductor ultra-fine particlesclassified in the differential electrical mobility classifier 303 aretransported into the depositing chamber 103 in conjunction with thecarrier gas via the ultra-fine particle depositing nozzle 401 to becollect a deposited on the depositing substrate 405. In addition, theultra-fine particle depositing nozzle 401 is controlled in temperatureby means of the heater 402, which is controlled and maintained at aconstant temperature (150 degrees Celsius) with the heater controller403. This makes it possible to prevent the ultra-fine particles fromdepositing in the nozzle pipe by making use of the thermo-phoresiseffect and thus improve the deposition efficiency.

[0100] At this time, the target 411 is excited with the excimer laserlight 408, and the transparent medium ejected through the ablationreaction is collected and deposited on the depositing substrate 405 atthe same time the high-purity semiconductor ultra-sine particles arecollected and deposited on the depositing substrate 405.

[0101] Here, controlling and maintaining the depositing chamber at aconstant pressure P2 (2.0 Torr) by the aforementioned means makes itpossible to deposit the transparent medium under the optimum condition.

[0102] Furthermore, it is made possible to maintain the pressure P2 at agiven value using the carrier gas exhaust system 309, which exhaustsonly part of the carrier gas 202 using a pump mainly by a turbomolecular pump and is controlled in accordance with the pressure P2 ofthe depositing chamber. This allows the difference in pressure betweenP1 and P2 to be made greater (P1=5.0 Torr, P2=2.0 Torr, the differencein pressure=3.0 Torr) than that achieved without the carrier gas exhaustsystem 309 (P1=5.0 Torr, P2=4.0 Torr, the difference in pressure=1.0Torr), making it possible to employ the pressure difference moreefficiently in the transportation of ultra-fine particles.

[0103] As described above, by collecting and depositing the classifiedhigh-purity semiconductor ultra-fine particles and the transparentmedium at the same time, it is made possible to fabricate the quantumdot functional structure, as shown in FIG. 9, having a sectionalstructure where the high-purity ultra-fine particles 501 having a singlediameter and uniform structure are homogeneously distributed in thetransparent medium 502.

[0104] Incidentally, here, the high-purity semiconductor ultra-fineparticles and the transparent medium are collected and deposited at thesame time in the depositing chamber 103. However, first, the high-puritysemiconductor ultra-fine particles may be deposited from the ultra-fineparticle depositing nozzle 401 to allow a certain amount of thehigh-purity semiconductor ultra-fine particles to be deposited.Thereafter, the transparent medium may be deposited on the depositionsubstrate, thereby forming a layer structure of the ultra-fine particlesand the transparent medium.

[0105] In the aforementioned procedures for fabricating the quantum dotfunctional structure, laser ablation is performed on the target 411 withthe excimer laser light 408 in the depositing chamber 103, therebydepositing the transparent medium. Unlike these procedures, thefollowing procedure may be employed. That is, first, the atmosphericrare gas 417 (A He gas of a purity of 99.999%) is introduced into thetransparent medium generating chamber 104 at a constant mass flow rateQT (0.5 l/min) via the mass flow controller 416. Then, in the subsequentstep, the transparent medium target 422 is excited with the excimerlaser light 420 (ArF excimer laser of wavelength 193 nm) which iscondensed through a condensing lens 418 and then introduced into thetransparent medium generating chamber 104 via the laser light inletwindow 419. Thereafter, in the following step, the transparent mediumcaptured from the transparent medium intake pipe 424, which is arrangedin the direction of growth of the ablation plume 423 excited with theexcimer laser light 420, is ejected from the transparent mediumdepositing nozzle 415 in the depositing chamber 103 and thus depositedon the depositing substrate 405. As described above, upon deposition, itis made possible to prevent the oxidation of semiconductor ultra-fineparticles sensitive to the ambient oxidative atmosphere by performing nolaser ablation on the transparent medium in the depositing chamber 103.

[0106]FIG. 11 is a view illustrating another example of the holder 404and the depositing substrate 405 to be used in the depositing chamber103 according to this embodiment. As shown in FIG. 11, the depositingsubstrate holder 404 and the depositing substrate 405 are adapted to berotatable about the center of the depositing substrate 405 so as to beparallel or orthogonal to each of the ultra-fine particle depositingnozzle 401, the transparent medium target 411, and the transparentmedium depositing nozzle 415. In addition, a direct current power supply703 is connected to the depositing substrate 405 to apply apredetermined voltage thereto.

[0107] For example, upon alternate deposition, such a configurationallows the angle of the depositing substrate 405 to rotate from thehorizontal by 45 degrees in the counterclockwise direction as shown inFIG. 11 (in the direction shown by the arrow S1) so as to be orthogonalto a deposition direction 451 of the ultra-fine particles during thedeposition of the ultra-fine particles. On the other hand, upondeposition of the transparent medium, the depositing substrate 405 ismade horizontal so as to be at 45 degrees to both the depositiondirection 451 of the ultra-fine, particles and a deposition direction452 of the transparent medium, that is, so as to be parallel to thetransparent medium target 411. It is thereby made possible to improvethe deposition efficiency of the ultra-fine particles and thetransparent medium and distribute ant the deposit homogeneously.

[0108] In addition, a bias voltage (e.g., 100V) is applied to thedepositing substrate 405 with a direct current power supply 453 tointroduce liquid nitrogen into a liquid nitrogen reservoir 454 and cooldown the depositing substrate 405 (e.g., to 100 degrees Celsius),thereby making it possible to improve the deposition efficiency of theultra-fine particles.

[0109] Here, upon collecting and depositing the high-puritysemiconductor ultra-fine particles, the micro-ammeter 414 can be used tomeasure as an electric current the electrons exchanged when theclassified and charged ultra-fine particles are collected and depositedon the substrate, thereby making it possible to check and control theamount of deposit of the ultra-fine particles.

[0110] As described above, it is possible to realize an apparatus forfabricating a quantum dot functional structure, which comprises thefollowing chambers and means. That is, the apparatus comprises a fineparticle generating chamber for generating fine particles, a fineparticle classifying chamber for classifying the fine particlesgenerated in the fine particle generating chamber according to thedesired particle diameter in a gas, gas exhaust means for exhausting thegas that transports the fine particles, and transparent mediumgenerating means for generating a transparent medium. The apparatus alsocomprises a depositing chamber for collecting the fine particlesclassified in the fine particle classifying chamber onto a substrate aswell as collecting the transparent medium generated by the transparentmedium generating means onto the substrate and depositing the classifiedfine particles and transparent medium onto the substrate. Using such anapparatus for fabricating a quantum dot functional structure, nm-sizedhigh-purity ultra-fine particles having a single diameter and uniformstructure can be fabricated efficiently with their contamination anddamage being alleviated and deposited on a deposition substrate. Inaddition, it is also made, possible to fabricate an opticallyfunctioning device which employs as the active layer the quantum dotfunctional structure having the ultra-fine particles distributedhomogeneously in the stable transparent medium.

[0111] (Second embodiment)

[0112] Now, as a second embodiment, an explanation is given to animproved disk type ultra-fine particle classifier which can be employedfor the fabrication of the quantum dot functional structure according tothe aforementioned first embodiment. The first embodiment employs thedifferential electrical mobility classifier 303 having a double cylinderstructure as the classifier. The classifier according to this embodimentis of a type different therefrom and an improved disk type ultra-fineparticle classifier.

[0113]FIG. 12 is a schematic sectional view illustrating theconfiguration of the disk type ultra-fine particle classifier accordingto the second embodiment of the present invention. This disk typeultra-fine particle classifier is constructed to have n+1 (where n is aninteger equal to or greater than 1) disks disposed concentrically inparallel to each other. The space between a first disk 601 and a seconddisk 602 defines a first classifying region 613; the space between thesecond disk 602 and a third disk 603 defines a second classifying region614; and similarly, the space between en nth disk 604 and an (n+1)thdisk 605 defines an nth classifying region 615. The first disk 601 hasannular guide slits 606 for introducing a carrier gas and ultra-fineparticles into said disk type ultra-fine particle classifier at theposition of radius r1. The second disk 602 has first annular slits 607at the position of radius r2 which is less than the radius r1. The thirddisk 603 has second annular slits 608 at the position of radius r3 whichis less than the radius r2. Similarly, the (n+1)th disk 605 has nthannular slits 610 at the position of radius r(n+1) which is less than aradius rn.

[0114] In addition, the first disk 601, the second disk 602, . . . , andthe (n+1)th disk 605 each have a sheath gas exhaust vent 611 forexhausting a first sheath gas 617, a second sheath gas 616, . . . , andan nth sheath gas 619 which flow from the periphery of the disks intothe first classifying region 613, the second classifying region 614, . .. , and the nth classifying region 615, respectively. Under the (n+1)thdisk 605, there is provided a carrier gas exhaust vent 612 forexhausting a carrier gas and classified ultra-fine particles. On thesecond disk 602, the circumference outer than the radius r2 and thefirst annular slits 607 is divided vertically into three portions. Theupper portion of the three-way divided portions can have a positive ornegative direct current voltage applied by a first direct current powersupply 620 thereto, and the lower portion is grounded. Moreover, themiddle portion is formed of an insulator 616 for insulating the upperand lower portions from each other, Similarly, on the (n+1)th disk 605,the circumference outer than the radius r(n+1) and the nth annular slits610 is divided vertically into three portions. The upper portion of thethree-way divided portions can have a positive or negative directcurrent voltage applied by an nth direct current power supply 622thereto, and the lower portion is grounded. Moreover, the middle portionis formed of an insulator 616 for insulating the upper and lowerportions from each other. In the disk type ultra-fine particleclassifier, all the constituent portions other than the three-waydivided portions of each of the disks from the aforementioned seconddisk 602 to the (n+1)th disk 605 are grounded.

[0115] Ultra-fine particles were classified by the following operationin the disk type ultra-fine particle classifier shown in FIG. 12. Thefirst sheath gas 617, the second sheath gas 618, . . . , and the nthsheath gas 619 are introduced from the periphery of each disk into thefirst classifying region 613, the second classifying region 614, . . . ,and the nth classifying region 615, respectively. Each of the introducedsheath gases passes through each classifying region in a laminar flowand then is exhausted from the sheath gas exhaust vent 611.

[0116] On the other hand, charged ultra-fine particles are transportedby a carrier gas to be introduced through the annular guide slits 606provided for the first disk 601 into the disc type ultra-fine particleclassifier and then ejected into the first classifying region 613. Inthe first classifying region 613, an electrostatic field is establishedby the first direct current power supply 620 between the first disk 601and the second disk 602 in a direction perpendicular to the direction ofthe first sheath gas flow. This causes the charged ultra-fine particlesejected from the annular guide slits 606 to be deflected from the firstdisk 601 toward the second disk 602 while being transported laterally bythe first sheath gas 617 and drawing an orbit according to theelectrical mobility which is dependent on the number of charges andparticle diameter.

[0117] Only those deflected charged ultra-fine particles that havereached the first annular slits 607 provided on the second disk 602 areclassified through the first classifying region 613 and then erected tothe second classifying region 614. In the second classifying region 614,an electrostatic field is established by a second direct current powersupply 621 between the second disk 602 and the third disk 603 in adirection perpendicular to the direction of the second sheath gas flow.This causes the charged ultra-fine particles ejected from the firstannular slits 607 to be deflected from the second disk 602 toward thethird disk 603 while being transported laterally by the second sheathgas 618 and drawing an orbit according to the electrical mobility Whichis dependent on the number of charges and particle diameter. Only thosedeflected charged ultra-fine particles that have reached the secondannular slits 608 provided on the third disk 603 are classified throughthe second classifying region 614 and then ejected to the thirdclassifying region.

[0118] Similarly, in the nth classifying region 615, an electrostaticfield is established by the nth direct current power supply 622 betweenthe nth disk 604 and the (n+1)th disk 605 in a direction perpendicularto the direction of the nth sheath gas flow. This causes the chargedultra-fine particles ejected from the (n−1) annular slits 609 to bedeflected from the nth disk 604 toward the (n+1)th disk 605 while beingtransported laterally by the nth sheath gas 619 and drawing an orbitaccording to the electrical mobility which is dependent on the number ofcharges and particle diameter. Only those deflected charged ultra-fineparticles that have reached the nth annular slits 610 provided on the(n+1)th disk 605 are classified through the nth classifying region 615and then taken out of the carrier gas exhaust vent 612.

[0119] In the disk type ultra-fine particle classifier shown in FIG. 12,the parameters (hereinafter referred to as the classifying parameters)related to the mean particle diameter and the classifying resolution ofultra-fine particles to be classified include the following parameters.That is, the parameters include the projected distance of the annularslits of the upper portion of a classifying region and the annular slitsof the lower portion of the classifying region (corresponding to thedifference of (rn-r(n+1)) in FIG. 12). The parameters also include thedistance between two disks defining a space or a classifying region, thedirect current voltage applied between two disks defining a space or aclassifying region, the type of a carrier gas, the flow rate of thecarrier gas, the type of a sheath gas, the flow rate of the sheath gas,and the like. Suppose that the same aforementioned classifyingparameters are employed for the first classifying region 613 to the nthclassifying region 615. In this case, all the classifying conditionsbecome the same (the mean particle diameter and the classifyingresolution of the ultra-fine particles to be classified). In otherwords, this means that the classifying resolution of the ultra-fineparticles classified in the first classifying region 613 will never beimproved even after the ultra-fine particles have passed through thesecond classifying region 614 and the nth classifying region 615.

[0120] In this context, the classifying parameter of each classifyingregion was made changeable, thereby making it possible to improve theclassifying resolution of the ultra-fine particles passing ,through themulti-stage classifying regions. More specifically, made changeable werethose classifying parameters such as the direct current voltage appliedto two disks defining a space or a classifying region, the flow rate ofa carrier gas, the flow rate of a sheath gas, and the type of the sheathgas. Now, a detailed explanation will be given below to a method forimproving the classifying resolution of ultra-fine particles by changingthe classifying parameters.

[0121] FIGS. 13(a) and 13(b) are schematic views illustrating therelationship between the number and diameter of the ultra-fine particlesclassified in each classifying region. As shown in FIG. 13(a), forexample, the ultra-fine particles classified in the first classifyingregion 613, strictly speaking, do not have a single diameter but have avariance of Δdp1 about the mean particle diameter dp1. The mean particlediameter of the classified ultra-fine particles is dependent on thedirect current voltage applied to the classifying region. Therefore, thedirect current voltage applied to the second classifying region 614 isslightly shifted toward the negative or positive side from the directcurrent voltage applied to the first classifying region 613, therebymaking it possible to shift slightly the mean particle diameter dp2 ofthe ultra-fine particles classified in the second classifying region 614from dp1. Accordingly, this causes the variance of Δdp2 about the meanparticle diameter dp2 to be slightly shifted from Δdp1. Therefore, forthe ultra-fine particles classified in the second classifying region, itis possible to reduce any one of the variances either of those havingparticle diameters greater than dp1 or of those having particlediameters less than dp1.

[0122] Furthermore, as shown in FIG. 13(b), the direct current voltageapplied to the third classifying region is slightly shifted toward thepolarity opposite to the polarity to which the direct current voltagewas shifted in the second classifying region 614, thereby making itpossible to reduce the variance opposite to that reduced in the secondclassifying region. As a result, this has made it possible to provide abetter classifying resolution than that of a disk type ultra-fineparticle classifier comprising only one-stage classifying region.

[0123] Incidentally, in the subsequent classifying regions following thethird classifying region, it is also possible to improve the classifyingresolution by repeatedly shifting the applied voltage slightly from thatof the classifying region in the previous stage in the same manner as inthe second and third classifying regions.

[0124] As described above, charged ultra-fine particles move at a speedthat in dependent on the particle diameter (i.e., the electricalmobility) in a direction perpendicular to disks from an upper disk to alower disk. At the same time, the particles move at a constanttransportation speed in conjunction with a sheath gas toward the centerof and in parallel to the disks. As a result, the ultra-fine particleshaving a particle diameter distribution and ejected from the annularslits of the upper disk into the classifying region are distributed inparticle diameter in parallel to and toward the center of the disksuntil the particles reach the lower disk. Only part of the ultra-fineparticles distributed in particle diameter are classified through theannular slits of the lower disk and then taken out. Therefore, toimprove the classifying resolution of ultra-fine particles, thedistribution of particle diameters in parallel to the disks and towardthe center of the disks should be made broader. In other words, the flowrate of the sheath gas should be made greater to make the transportationspeed of the ultra-fine particles higher.

[0125] In this context, in the disk type ultra-fine particle classifiershown in FIG. 12, the flow rate of the sheath gas was made changeable ineach classifying region and the classifying resolution was also madechangeable. Furthermore, the flow rate of the second sheath gas was madehigher than, that of the first sheath gas; the flow rate of the thirdsheath gas was made higher than that of the second sheath gas; . . . ;and the flow rate of the nth sheath gas was made higher than that of the(n−1)th sheath gas, thereby making it possible to gradually improve theclassifying resolution. As a result, it was made possible to providebetter classifying resolution than that of the disk type ultra-fineparticle classifier comprising only one-stage classifying region.

[0126] For nm-sized ultra-fine particles, diffusion caused by theBrownian movement cannot be neglected in their transport process. In thedisk type ultra-fine particle classifier shown in FIG. 12, the chargedultra-fine particles flowing from the annular slits of the upper diskinto the classifying region are subjected to the diffusion caused by theBrownian movement until the particles reach the lower disk according totheir individual electrical mobility. The Brownian movement causes theultra-fine particles to diffuse totally at random (i.e., totallyindependent of the particle diameter) either in the direction of theflow of the sheath gas (i.e., from the periphery to the center of thedisk) or in the opposite direction (i.e., from the center to theperiphery of the disk). Therefore, the diffusion due to the Brownianmovement in the classifying region causes the classifying resolution ofultra-fine particles to be reduced.

[0127] In general, the diffusion coefficient of the ultra-fine particlessubjected to the diffusion due to the Brownian movement in a gasdecreases with increasing viscosity of the gas. In addition, thediffusion coefficient decreases as the collision diameter of the gasatoms and molecules increases. Therefore, it is made possible to improvethe classifying resolution of ultra-fine particles by selecting a sheathgas having high viscosity or a gas having larger collision diameters asthe sheath gas flowing through the classifying region.

[0128] In this context, in the disk type ultra-fine particle classifiershown in FIG. 12, a He gas was used as the first sheath gas 617 in thefirst classifying region 613 and an Ar gas was used as the second sheathgas 618 in the second classifying region 614. Here, the He gas has a gasviscosity of 19.6×10⁻⁶ Pa·s and a gas atom collision diameter of2.15×10⁻¹⁰ m, while the Ar gas has a gas viscosity of 22.3×10⁻⁶ Pa·s anda gas atom collision diameter of 3.58×10⁻¹⁰ m (where the gas viscosityis given under a pressure of 1 atm at a temperature of 20 degreesCelsius). This made it possible to exert less effect of the Browniandiffusion on the ultra-fine particles of the second classifying region614 than those of first classifying region 613. As a result, it was madepossible to improve the classifying resolution than that of the disktype ultra-fine particle classifier comprising only one-stageclassifying region.

[0129] Incidentally, it is made also possible to further improve theclassifying resolution of ultra-fine particles by employing, as thesheath gas, a gas of a much higher gas viscosity or a much largercollision diameter in the third classifying region and the subsequentclassifying regions. For example, this can be achieved by using a Kr gas(of a gas atom collision diameter of 4.08×10⁻¹⁰ m) as the third sheathgas in the third classifying region and a Xe gas (of a gas atomcollision diameter of 4.78×10⁻¹⁰ m) as the fourth sheath gas in thefourth classifying region.

[0130] The flow rate of a carrier gas for transporting ultra-fineparticles also has effect on the classifying resolution of theultra-fine particles. The carrier gas flows into a classifying regionfrom the annular slits of the upper disk in conjunction with theultra-fine particles. A higher flow rate of the carrier gas would give ahigher initial speed to the ultra-fine particles, flowing into theclassifying region from the upper annular slits, in the direction fromthe upper disk to the lower disk. The aforementioned direction of theinitial speed equals to the direction of the speed caused by theelectrical mobility. This causes an error corresponding to the magnitudeof the aforementioned initial speed to occur in the distance over whichthe ultra-fine particles move from the upper to the lower disk, therebyreducing the classifying resolution.

[0131] On the other hand, a lower flow rate of the carrier gas wouldpresent a problem of the occurrence of mutual association and cohesionof the ultra-fine particles due to the Brownian diffusion. The higherthe initial concentration of the ultra-fine particles and the smallerthe initial particle diameter, the earlier in time the aforementionedcohesion takes place. In the process in which nm-sized ultra-fineparticles generated somehow are transported to the disk type ultra-fineparticle classifier shown in FIG. 12, a longer time of transportationcauses the particle diameter to be changed due to the mutual associationand cohesion of the ultra-fine particles before the particles areclassified in the disk type ultra-fine particle classifier. To preventthis from taking place, it is necessary to increase the flow rate of thecarrier gas for transporting the ultra-fine particles to shorten theaforementioned transportation time.

[0132] In order to solve the aforementioned mutually contradictory twoproblems (i.e., a reduction in classifying resolution at a high flowrate of the carrier gas and cohesion taking place at a low flow rate ofthe carrier gas), the flow rates of a carrier gas flowing into eachclassifying region were made different from each other in the disk typeultra-fine particle classifier shown in FIG. 12. Then, the ultra-fineparticles were classified in the following procedure. The flow rate ofthe carrier gas flowing from the annular guide slits 606 of the firstdisk 601 into the first classifying region 613 was made higher, therebypreventing the effect of the cohesion taking place until the generatedultra-fine particles are transported to the disk type ultra-fineparticle classifier. The particle concentration of the ultra-fineparticles classified in the first classifying region 613 is lower thanthat of the particles upstream of the annular guide slits 606. That is,the ultra-fine particles classified in the first classifying region 613require a longer time for cohesion than the ultra-fine particlesupstream of the annular guide slits 606. Therefore, the flow rate of thecarrier gas flowing from the first annular slits 607 into the secondclassifying region 614 was made lower than the flow rote of the carriergas flowing into the first classifying region 613, thereby providing animproved classifying resolution. As described above, the flow rate of acarrier gas flowing in from annular slits was made lower toward the endstage of classifying region, thereby solving the problem of mutualcohesion and a reduction in classifying resolution of the ultra-fineparticles.

[0133] Nm-sized ultra-fine particles are very sensitive to thecontamination of impurities due to less number of constituent atoms anda high ratio of the number of atoms exposed to the surface to that ofinternal atoms. In this context, in the disk type ultra-fine particleclassifier shown in FIG. 12, the insulator 616 was formed of aceramic-based substance and all other portions were formed of metal,thereby making it possible to bake the ultra-fine particle classifier athigh temperatures under a high vacuum. This made it possible to keep theinside of the ultra-fine particle classifier clean and preventimpurities from finding their way Into the ultra-fine particles.

[0134] The present Invention has been explained in terms of preferredembodiments illustrated in the accompanying drawings. However, it isobvious for those skilled in the art that variations and modificationsmay be readily made to the invention. It is to be understood that allsuch variations are intended to be within the scope of the invention.

What is claimed is:
 1. An apparatus for fabricating a quantum dotfunctional structure comprising a fine particle generating chamber forgenerating fine particles, a fine particle classifying chamber forclassifying the fine particles generated in said fine particlegenerating chamber according to a desired particle diameter in a gas,gas exhaust means for exhausting a gas for transporting said fineparticles, transparent medium generating means for generating atransparent medium, and a depositing chamber for collecting the fineparticles classified in said fine particle classifying chamber onto asubstrate as well as for collecting the transparent medium generated bysaid transparent medium generating means onto said substrate and fordepositing said classified fine particles and said transparent mediumonto said substrate.
 2. The apparatus for fabricating a quantum dotfunctional structure according to claim 1 , wherein transparent mediumgenerating means is composed of first transparent medium generatingmeans arranged in the depositing chamber, and a second independenttransparent medium generating chamber.
 3. The apparatus for fabricatinga quantum dot functional structure according to claim 1 , wherein thefine particle generating chamber, the fine particle classifying chamber,and a transport path of fine particles in the depositing chamber areconstructed on a straight line.
 4. The apparatus for fabricating aquantum dot functional structure according to claim 1 , wherein apressure of the fine particle generating chamber and a pressure of thedepositing chamber are controlled independently.
 5. The apparatus forfabricating a quantum dot functional structure according to claim 1 ,wherein the gas exhaust means is controlled in accordance with apressure of the depositing chamber.
 6. The apparatus for fabricating aquantum dot functional structure according to claim 1 , wherein thesubstrate in the depositing chamber is rotatable with respect to adirection of deposition of the fine particles and transparent medium. 7.The apparatus for fabricating a quantum dot functional structureaccording to claim 1 , further comprising a temperature controlmechanism being capable of maintaining a transport path of fineparticles at a constant temperature.
 8. The apparatus for fabricating aquantum dot functional structure according to claim 1 , wherein at leastone of the fine particles and the transparent medium is generated usinglaser ablation, and a plasma plume produced upon generation is observedusing a charge coupled device.
 9. The apparatus for fabricating aquantum dot functional structure according to claim 1 , wherein at leastone of the generated fine particles and the transparent medium isradiated with ultraviolet light to observe fluorescent light.
 10. Theapparatus for fabricating a quantum dot functional structure accordingto claim 1 , further comprising an ultra-fine particle classifierwherein a classifying region employs a space defined between twoconcentric disks, spaced apart from each other and arranged in parallelto each other; charged ultra-fine particles are classified in saidclassifying region by raking use of electrical mobility being dependenton a particle diameter of charged particles upon application of anelectrostatic field thereto in a viscous fluid; and three or more ofsaid concentric disks are arranged to thereby constitute saidclassifying region by two or more multi-stages.
 11. The apparatus forfabricating a quantum dot functional structure according to claim 10 ,wherein a direct current voltage can be individually applied to eachstage of a multi-stage classifying region.
 12. The apparatus forfabricating a quantum dot functional structure according to claim 10 ,wherein a disk for partitioning the multi-stage classifying region isprovided with slits for allowing a carrier gas to flow from oneclassifying region into another classifying region.
 13. The apparatusfor fabricating a quantum dot functional structure according to claim 12, wherein the carrier gas flows at different flow rates into each stageof the multi-stage classifying region.
 14. The apparatus for fabricatinga quantum dot functional structure according to claim 12 , wherein asthe number of stages of the multi-stage classifying region increases, aflow rate of the carrier gas flowing into each stage decreases.
 15. Theapparatus for fabricating a quantum dot functional structure accordingto claim 10 , wherein a sheath gas flows from a periphery portion of thedisk toward a central portion of the classifying region.
 16. Theapparatus for fabricating a quantum dot functional structure accordingto claim 15 , wherein different types of the sheath gas are employed ineach stage of the multi-stage classifying region.
 17. The apparatus forfabricating a quantum dot functional structure according to claim 15 ,wherein as the number of stages of the multi-stage classifying regionincreases, viscosity or a collision diameter of the sheath gas of eachstage increases.
 18. The apparatus for fabricating a quantum dotfunctional structure according to claim 15 , wherein the sheath gasflows through each stage of the multi-stage classifying region atdifferent flow rates.
 19. The apparatus for fabricating a quantum dotfunctional structure according to claim 18 , wherein as the number ofstages of the multi-stage classifying region increases, a flow rate ofthe sheath gas flowing into each stage increases.
 20. The apparatus forfabricating a quantum dot functional structure according to claim 10 ,wherein the disk is formed of ceramic-based insulator and metal.
 21. Theapparatus for fabricating a quantum dot functional structure accordingto claim 1 , having an ultra-fine particle classifier comprising: aplurality of disks, arranged concentrically in parallel to each other,for defining therebetween a multi-stage classifying region forclassifying the ultra-fine particles; slits, formed on said disks, forintroducing a carrier gas and the ultra-fine particles into a subsequentstage classifying region through each of the disks, a sheath gas exhaustvent, provided at an axis portion of each disk, for exhausting thesheath gas flowing from a periphery of each disk into each classifyingregion, and a carrier gas exhaust vent, provided on a lower portion ofthe last stage disk, for exhausting a carrier gas and classifiedultra-fine particles, said ultra-fine particle classifier classifyingcharged ultra-fine particles in said classifying regions.
 22. Theapparatus for fabricating a quantum dot functional structure accordingto claim 21 , wherein a circumferential portion of the disk outer thanthe slits is divided into three portions vertically with respect to asurface of the disk, an upper portion of the three-way divided portionof said disk having a direct current voltage applied thereto, the lowerportion thereof being grounded, and the middle portion thereof beingconstructed to electrically insulate the upper and lower portions fromeach other.
 23. A quantum dot functional structure fabricated by theapparatus for fabricating a quantum dot functional structure accordingto any one of claims 1 to 10 .
 24. An optically functioning deviceemploying the quantum dot functional structure according to claim 23 asan active layer.
 25. A method for fabricating a quantum dot functionalstructure comprising the steps of: generating fine particles,classifying said fine particles generated according to a desiredparticle diameter in a gas, exhausting the gas for transporting saidfine particles after said classifying step, collecting said classifiedfine particles onto a substrate and generating a transparent medium atthe same time, and depositing said classified fine particles and saidtransparent medium onto said substrate at the same time.
 26. The methodfor fabricating a quantum dot functional structure according to claim 25, wherein the transparent medium is generated using, at the same time oralternately, any one of or both first transparent medium generatingmeans, disposed in a depositing chamber for depositing the fineparticles and the transparent medium, and second transparent mediumgenerating means arranged independently.
 27. The method for fabricatinga quantum dot functional structure according to claim 25 , wherein thefine particles and the transparent medium are controlled independentlyof each other so that each pressure upon generation thereof becomesoptimum at the same time, and thereby generated.
 28. The method forfabricating a quantum dot functional structure according to claim 25 ,wherein the gas for transporting fine particles is exhausted, after thestep of classifying the fine particles, in accordance with a pressure ofthe depositing chamber for depositing the fine particles and thetransparent medium onto the substrate.
 29. The method for fabricating aquantum dot functional structure according to claim 25 , furthercomprising the step of maintaining a path of the fine particles at aconstant temperature after the step of classifying the fine particles.30. The method for fabricating a quantum dot functional structureaccording to claim 25 , further comprising the step of observing, usinga charge coupled device, a plasma plume produced when at least one ofthe fine particles and the transparent medium is generated using laserablation.
 31. The method for fabricating a quantum dot functionalstructure according to claim 25 , further comprising the step ofobserving fluorescent light from said fine particles and saidtransparent medium, emitted when at least one of said fine particles andsaid transparent medium is radiated with ultraviolet light upongeneration thereof.
 32. A quantum dot functional structure fabricated bythe method for fabricating a quantum dot functional structure accordingto any one of claims 25 to 31 .
 33. An optically functioning deviceemploying the quantum dot functional structure according to claim 32 asan active layer.